I used Krylon Flat for a while, but my results were not consistently good. I had some very complicated directions from another wargamer. Only spray in one direction. Do multiple light coats and on and on.
I strongly agree with those above recommending Winsor Newton.
Here is part of a post I did when a Dullcote question came up in the past:
Then I tried Winsor & Newton Professional Matt Spray Varnish. I started using it since at least 2017.
Here are the results after spraying 100s of figures and lots of vehicles, buildings, earthworks and other terrain pieces.
Temperature in the 40s F – dried flat.
Temperature in the low 90sF – dried flat.
Humidity 92 per cent – dried flat.
Thick coat – dried flat.
Thin coat – dried flat.
Sprayed clear gloss (Krylon or Rustoleum) at 1:30 pm and W/N Matt at 4:00 pm, same day, – dried flat.
It has never, ever failed me.
My experience with clear sprays made in the US is that "matt" or "matte" usually means semi-gloss or satin. W/N is made in Britain and matt means perfectly flat.
The price from Dick Blick is very good. It has always been discounted. I have not price checked for a while, but the last time I did I found Dick Blick's discounted price is $9.56 USD for 400 ml (13.53 ounces according to Siri). That is less than 71 cents an ounce.
The cheapest I saw Dullcote was 3 ounces for $4.77 USD. That is over $1.59 USD per ounce!!
I read at least one post saying W/N was more expensive than Dullcote. The price per can is a lot more, but you get a whole lot more.
Here is a link to the product at Dick Blick:
link
Don't be put off by the warning that the paint has to dry for at least 6-12 months before applying the product to the paint. That may be for artists oils which take an extremely long time to thoroughly dry unless a drier is added. I do it within hours of my gloss coat which I put on the day after I finish my painting.
I sent Winsor & Newton an email asking about shelf life as I intended to buy six cans at a time. The response indicated that the question was interpreted to mean a can that had been started. The answer was that there was no known shelf life limitation. What I bought in April of 2018 is still fine.
If you try it, I hope your results are as good as mine.
Tom